Tell us what happened and you will get a reply from a person.
Before the first roll the app shows a fingerprint of the dice lock. When the game ends it reveals the key. Any SHA-256 tool will turn the key back into the fingerprint you saw, and the rolls listed with it are the rolls you got. In a game against a friend each phone contributes half of the key, so neither side can steer the dice.
Games with a friend go through Apple's Game Center. Both phones need to be signed in to Game Center in Settings. Invitations arrive as Game Center notifications; if one does not, check that notifications are allowed for Game Center on the invited phone.
A game in progress is saved on the phone and survives closing the app. Deleting the app deletes it. Games with a friend live in Game Center and reappear when you sign in again.
Purchases are handled by Apple. Ask for a refund at reportaproblem.apple.com; we cannot issue one ourselves.